tady je hezky rozepsaný všechno......If the Dothraki had not charged, they would have found themselves pinned against the infantry, their mobility lost. If they had moved right or left in search of Team Dead’s flanks, they would have run the risk of being flanked themselves (Team Dead also had cavalry, and its infantry was fast and fearless) or destroyed by Viserion and the Night King.
https://slate.com/culture/2019/04/battle-winterfell-military-analysis-tactics.html